Temperature actuated electrical switch

ABSTRACT

A temperature-actuated electrical switch of minimum size and dimension having a flattened conical tip portion insertable through a minimum sized opening in an engine block or container of fluid of variable temperature and featuring a tapered, reedtype electrical contact element of increased strength and stability and vibration attenuating characteristics.

' United States Patent Inventor Harry I. Baker Ann Arbor, Mich. Appl. No. 854,674

Filed Sept. 2, I969 Patented Aug. 24, I971 Assignee Chrysler Corporation Highland Park, Mich.

TEMPERATURE ACTUA'IED ELECTRICAL SWITCH 1 Claim, 5 Drawing Figs.

US. Cl 1. 337/380, 337/379 Int. Cl .4 "01h 37/04,

I-IOIh 37/20, HOI h 37/52 FieldofSearch 337/1,1I1, l 12, 379, 380

Primary Examiner-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorney-Hamess, Talburtt and Baldwin ABSTRACT: A temperature-actuated electrical switch of minimum size and dimension having a flattened conical tip portion insertable through a minimum sized opening in an engine block or container of fluid of variable temperature and featuring a tapered, reed-type electrical contact element of increased strength and stability and vibration attenuating characteristics.

TEMPERATURE ACTUATED ELECTRICAL SWITCH BACKGROUND OF THE INVENTION This invention relates to an electrical switch and, more particularly to a temperature actuated switch, specially suited for use in vibration subjected environments such, for example, as automobile type engines.

Prior forms of temperature-actuated switches employed in such environments have exhibited a mechanical resonance and a high sensitivity to induced mechanical vibrations occurring over the range of vibration frequencies encountered in the operation of automobile-type engines. In consequence, such switches have been found to be of erratic operation and to provide erroneous information signalling a warning condition when none, in fact, exists.

Accordingly, the present invention has among its objects to provide an improved form of temperature-actuated switch specially suited for use in vibration subjected environments.

A related object is to provide an improved form of temperature-actuated switch employing a reed-type contact switch element exhibiting a decreased sensitivity to vibration as a free reed.

A related object is to provide a temperature-actuated switch having a flexure-type thermostatic contact element of increased strength and stability and vibration attenuating characteristics.

Another object is to provide a temperature-actuated switch using a thermostatic contact element of increased thermal sensitivity and responsiveness.

Another object is to provide an improved form of temperature-actuated switch of minimum size and dimension and insertable through a minimum sized opening in an engine block or container of fluid of variable temperature.

SUMMARY Toward the accomplishment of the above and other objects, the invention provides a temperature-actuated electrical switch comprising an electrically and thermally conducting casing having a conically formed flattened tip portion of controlled lateral dimension. The tip portion is flattened about and clamps one end of a strip of thermostatic metal interiorly thereof and, by reason of its controlled lateral dimension, is adapted to be inserted through a minimum sized opening in a vessel or fluid container and into contact with a fluid of variable temperature therein. The strip constitutes the movable contact element of the electrical switch and is of progressively diminishing mass along its longitudinal extent from the secured end of the strip to its attenuated tip portion located adjacent a fixed electrical contact, which is electrically insulated from and has a terminal portion extending exteriorly of the casing.

The structure, operation and advantages of the switch device will be understood from consideration of the detailed description of a preferred embodiment of the invention made with reference to and following the accompanying DESCRIPTION OF THE DRAWINGS in which the illustrations of the switch device are of substantially enlarged scale for purposes of clarity and illustrating details of construction and wherein FIG. 1 illustrates an environment and an electrical signal warning circuit in which the temperature-actuated switch device of the present invention is employed;

FIG. 2 is a still greater enlargement and longitudinal sectional view of a temperature-actuated electrical switch device in accordance with the present invention taken in the direction 2-2 of Fig. 1;

FIG. 3 is a fragmentary and longitudinal sectional view with parts broken away taken in the direction 33 of FIG. 2;

FIG. 4 is a transverse sectional view taken in the direction 4-4 of FIG. 2; and

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to Fig. l of the drawings, the disclosed temperature-actuated switch is a pluglike device 10 adapted to be threadably received and supportingly mounted in a fluid container, such as the head or block 12 of an automobile engine with the tip portion of the plug immersed in the heated fluid or engine coolant 16 of variable temperature. At its opposite end located outside of the block, the plug is provided-with an electrically insulated terminal stud 18 for connecting it in an electrical circuit with an electrically powered utilization element, shown as a signal lamp device 20 which is energized from the negatively grounded vehicle storage battery 22 through a control switch, as the vehicle ignition switch 24. In the illustrated environment, the device 10 responds to the temperature of the engine coolant fluid to complete an electrical energizing circuit from the positive side of the battery 22 through the ignition switch 24 to one side or terminal of the warning device 22, the other side or terminal of which is returned through the switch to the electrically grounded engine block should the temperature of the coolant rise above a predetermined temperature.

As shown in Figs. 2, 3 and 4 the device 10 comprises a hollow, elongated metallic casing 30 enclosed at one end thereof, a reedlike element 32 formed of an elongated strip of thermostatic metal, and the above-mentioned terminal stud 18 projecting into the interior of the casing from the other end thereof and carrying an electrical contact element on the inner end thereof.

The casing 30 is a one-piece unitary structure formed of suitable electrically and thermally conducting metal, such as brass, and comprises a generally conically shaped portion 40, an externally threaded body portion 42, a hexagonally shaped portion 44 and a cylindrical collar portion 45. The enclosed end of the casing is a thin wall extruded section terminating in a blunt tip 46, which is subsequently flattened about and spot welded to one end of the reed strip 32 received within the interior of the casing. The body portion 42 is shown as provided with a standard pipe thread thereon and as being of relatively thick wall construction together with the hexagonally shaped portion 44 to withstand the stresses applied thereto to mount the plug in an internally threaded opening 13 in the head 12 of the engine block or container of heated fluid. At the open end of the casing, the collar portion 45 thereof is of a greater internal diameter or bore 47 than that of the cylindrical bore 48 extending through the body portion of the casing to form an annular seat or land 49 intermediate the casing ends.

The element 32 is composed of thermostatic metal such as bimetal or trimetal and deflects or changes its position in accordance with the temperature to which it is exposed. The strip has a flat base or end portion 50 conforming generally to the shape of the casing tip portion which securely clamps the base portion of the strip in the casing tip portion enveloping and engaging both sides of the base strip portion of the strip as shown in Fig. 4. The strip extends generally longitudinally of the interior of the casing and is of or assumes a slight dish shape as shown in Fig. 5. In accordance with the present invention, the strip is of progressively and unifonnly diminishing transverse dimensioned width from its secured base portion toward its tip 52. Affixed to the substantially pointed tip of the strip is an electrically conducting wire contact element 54 which engages and contacts the fixed electrical contact element of the terminal stud 18 at a predetermined temperature selected for actuation of the switch.

The externally threaded terminal stud 18 is formed of electrically conducting metal and has an enlarged annular flange portion 56 intermediate its ends and a reduced end portion 58 having a small end bore 59 therein which receives and is externally circumferentially crimped about the stem portion 60 of a disc-shaped contact button 62. In assembling the terminal stud electrode from the casing, is received on the stud, and the outer circumferential edge of the collar portion 45 is turned inwardly to secure the electrode to the casing, as shown at 68.

To calibrate the switch, the tip is heated to the temperature selected for actuation of the switch, say 242 F. for example, and the flattened tip of the casing is bent out of the axial plane of the casing as necessary to position the wire contact element at the tip of the strip in physical and electrical contact engagement with the edge of the contact button 62. When the strip cools, the strip assumes the position illustrated in Fig. 3 with the tip and contact element 54 adjacent and resiliently bearing or biased against the inner wall of the casing.

By reason of its tapered configuration, the natural resonance frequency of the strip has been found to have been increased and the tendency of the strip to vibrate as a free reed to have been considerably lessened. It will be appreciated -tureof maximum strength and stability and vibration attenuating characteristics. Also, the generally isosceles shape of the strip results in a more efficient utilization of the thermostatic material and increases the thermal sensitivity and responsiveness of the strip as-cpmpared to a rectangular strip of uniform width, the thermal capacity of the excess of material on the opposite sides of the longitudinal axis of which tends to delay the thermal responsiveness of the rectangular strip.

7 By reason of the conical formation of the enclosed end portion of the casing, the lateral expansion of the flattened tip portion 46 iscontrolled and prevented from flaring outwardly and assuming a fishtail or fan-shaped configuration, as would otherwise be encountered were the casing of cylindrical instead of conical formation. Thus, the maximum lateral dimension of the tip portion of the casing is controlled to be of a minimum dimension and to be less than that of the externally threaded body portion, which, in turn, can be of minimum size, requiring a minimum or smaller sized opening in the engine block in which the pluglike switch device is received.

I claim: l. A temperature actuated, reed-type electrical switch operable in a vibration-subjected environment and comprising a one-piece, elongated hollow metallic casing having a threaded body portion adapted to be received in a minimum-sized threaded opening in a liquid container and an integrally formed, conically shaped tip portion enclosed at one end thereof and adapted to be surrounded by a liquid medium of variable temperature within said container, an electrical contact insulated from and projecting axially centrally into the interior of the casing from the opposite end thereof, and an elongated strip of thermostatic metal secured at one end interiorly of and to the tip portion of the casing,

said strip being of progressively diminishing mass in its generally longitudinal extent from its secured end to a point at its tip positioned to engage the contact at a selected temperature for actuation of the switch,

said tip portion of said casing having a spadelike configuration flattened about and providing a support for the secured end of said strip portion therein and being of decreased transverse dimension in its longitudinal extent from its threaded body portion towards its enclosed tip portion to facilitate insertion thereof through said minimum sized threaded opening in said liquid container. 

1. A temperature actuated, reed-type electrical switch operable in a vibration-subjected environment and comprising a one-piece, elongated hollow metallic casing having a threaded body portion adapted to be received in a minimumsized threaded opening in a liquid container and an integrally formed, conically shaped tip portion enclosed at one end thereof and adapted to be surrounded by a liquid medium of variable temperature within said container, an electrical contact insulated from and projecting axially centrally into the interior of the casing from the opposite end thereof, and an elongated strip of thermostatic metal secured at one end interiorly of and to the tip portion of the casing, said strip being of progressively diminishing mass in its generally longitudinal extent from its secured end to a point at its tip positioned to engage the contact at a selected temperature for actuation of the switch, said tip portion of said casing having a spadelike configuration flattened about and providing a support for the secured end of said strip portion therein and being of decreased transverse dimension in its longitudinal extent from its threaded body portion towards its enclosed tip portion to facilitate insertion thereof through said minimum sized threaded opening in said liquid container. 